Paul, generally it takes a pretty long while for classical works to be established as claasic or important pieces, and that might be the issue with those two works. I could find a mention of "Für Alina" in any of the sources I use, and only one mention of "Spiegel im Spiegel". According to that source, the latter is a cello sonata. From what I gather, it seems that Part is more noted for orchestral and choral music than for solo piano music.
Yeah, he probably is. Anyway thanks for the answer. Had to check what you said about "Spiegel im Spiegel". Apparently it was originally written for piano and violin. I didn't know that at all, only knew it as a solo piano piece. But Pärt often changed the instrumentation of his works, so it doesn't really surprise me.